When a ball is struck by a racket such as a tennis racket or racquetball racket, the racket bends and begins to vibrate. Since the vibration is produced when the player is gripping the racket, the vibration is translated to the player's arm. The degree of vibration imparted to the player's arm varies depending upon the racket material and construction.
Racket vibrations can be classified into several modes amongst which are three vibratory modes which normally affect the quality of play. A first mode, illustrated in FIG. 1, comprises a first bending mode of the racket frame and string. A second mode, depicted in FIG. 2, comprises a second bending mode of both the frame and strings. A third mode shown in FIG. 3 comprises the vibration of the strings in a plane perpendicular to the plane of the racket.
The vibrations would continue in absence of any damping property of the racket. Damping, for the purpose of this application, is defined as the dissipation of energy. Despite the natural intrinsic damping of the rackets, the vibrations are still discomforting to a player. Therefore, attempts have been made to increase the damping of the racket. For example, U.S. Pat. No. 4,609,194 to Krent et al. and U.S. Pat. No. 4,368,886 to Graf teach the use of inserts which dampen the vibration of strings. Although the inserts described in U.S. Pat. No. 4,609,194 and U.S. Pat. No. 4,368,886 have proven to be successful for damping string vibration, they have not proven satisfactory for damping the first and second modes of vibration hereinafter referred to as "frame vibration" which has proven to be more discomforting to a player. Frame vibration is more discomforting to a player than string vibration because the energy associated with such vibration is greater than string vibration and is directly translated to the player's arm.
U.S. Pat. No. 4,875,679 to Movilliat et al. describes one method of damping frame vibration. In this method, Movilliat et al. secures damping elements comprising viscoelastic material to very specific and relatively small portions of the racket. In particular, the damping elements are secured to the bridge of the racket or on both sides of the bridge. They can also be secured to the head or on both sides of the head. In addition, Movilliat teaches that damping elements can be centrally secured on both sides of the head. Although providing some damping affect, the Movilliat et al. racket provides less than optimal damping results.
U.S. Pat. No. 4,983,242 to Reed discloses yet another method of damping frame vibration. Reed teaches the use of a tennis racket frame comprising an inner tubular member and an outer tubular member. Sandwiched between the two tubular members is a dampening sleeve made of viscoelastic material. The sleeve is coextensive with both the tubular members. This racket is unsatisfactory because it is 20% weaker than a tubular racket because as Reed shows, the first modal frequency decreases from 55 to 50 Hz. In addition, Reed unnecessarily uses viscoelastic material thereby increasing the weight and cost of the racket.
Thus, there currently exists a need for a better solution than any disclosed above in order to substantially dampen the frame vibration of a racket.